Democratic presidential nominee Walter F. Mondale today sharpened his attack on the Republican Party over the issue of the separation of church and state, accusing the GOP of flirting with a mixture of religion and government that would "corrupt our faith and divide our nation."

"The Republicans in Dallas raised doubts whether they respect the wall our founders placed between government and religion," Mondale said today in his regular weekly paid radio address.

"In America, our faith has always been intensely personal. It is between the individual and God, between families and their churches and synagogues, with no room for politicians in between," he said.

"Government must not be permitted to dictate the religious life of our people," Mondale said. "If that force is unleashed, it will corrupt our faith and divide our nation. That future is not the American way."

Today's statement marked the third time in eight days that Mondale has addressed the question of church and state and the first time that he has named the GOP. He has not mentioned President Reagan by name.

Religious fundamentalists played a prominent role at the Republican National Convention in Dallas last month, pressing successfully to include provisions in the GOP platform supporting prayer in schools and tuition tax credits, and opposing abortion.

At a prayer breakfast on the day he accepted the nomination, Reagan said, "Politics and morality are inseparable, and as morality's foundation is religion, religion and politics are necessarily related . . . . Without God, democracy will not and cannot endure."

Speaking to reporters on the White House lawn before leaving for California today, Reagan said, "I was speaking about people who would deny such things as chaplains in the military. I'm not seeking to install a state religion in any way."

Three days after Reagan's remarks in Dallas, Mondale made the first of his verbal attacks, emphasizing that he believed religion should be personal and kept out of politics, then telling his audience at a fund-raising event in Dallas that such a separation was made explicitly clear in the Constitution.

Each statement, however, has been more pointed, and aides say Mondale will make major statements on the subject in separate addresses to B'nai B'rith and the predominantly black National Baptist Convention meeting in Washington on Thursday.

Last week, Reagan campaign director Edward J. Rollins said that religion is "not going to be an issue any more than it has been. I think Mondale runs a real risk if he tries to make it more of an issue. It's not a campaign theme of ours."

Mondale campaign press secretary Maxine Isaacs said today, "It's a deep issue. It's a topic of considerable interest. I don't know if it's a voting issue. But is it a subject for a great American debate? Absolutely."

Governors, mayors, business executives and others have peppered the Democratic candidate with advice on the subject since the GOP convention, and have urged Mondale, the son of a Methodist minister, to take on the Republicans on this issue.

Today's radio address was not focused primarily on religion, however. Mondale attacked Reagan on a wide range of subjects and the stances taken on them in the Republican platform.

Afterwards, he told reporters he was not dismayed by polls showing him well behind Reagan on the eve of the Labor Day kickoff of final head-to-head campaigning.

He also accused the Reagan administration of "diplomacy by megaphone," of shouting at the Soviet Union and other countries instead of trying earnestly to create dialogue.